Ultraviolet rays reaching the surface of the earth are only 6% of the rays of the sun, but cause degradation in quality such as coloring, fading, lowering of strength, or destruction of rubbers, paints, inks, etc. For preventing such degradation caused by ultraviolet rays, ultraviolet absorbers are incorporated in various products into which these products and materials are compounded.
Also on human skin, ultraviolet rays cause skin acute reaction such as sun burn or sun tan, and, on a long-term basis, skin aging or cancer. In view of these points, development of sunscreen cosmetics in which an ultraviolet absorber or an ultraviolet-scattering agent is compounded has actively been made, and various preparations are sold.
Ultraviolet absorbers compounded in these preparations are classified, based on their structure, into cinnamic acid-type, PABA-type, benzophenone-type, salicylic acid-type, heterocyclic-type, camphor-type, dibenzoylmethane-type, chalcone-type, etc., and many ultraviolet absorbers have been developed. However, ultraviolet absorbers used for human skin are restricted in view of safety, touching in use, solubility thereof into the base in compounding in sunscreen cosmetics, etc., and among many so far developed ultraviolet absorbers, cinnamic acid-type and benzophenone-type ultraviolet absorbers are frequently used in skin external preparations.
As an invention which started from a motive of substituting a natural antioxidant for BHT in preparations being to contact with human bodies, an invention in which para-methoxycinnamic esters are stabilized using tocopherol is known (Japanese Laid-open Patent Publication 9-104856). Therein, it is only α-tocopherol that is specifically exemplified as the tocopherol.
Among cinnamic acid-type ultraviolet absorbers, ultraviolet absorbers containing a para-methoxycinnamic ester are mainly used, and as an example, 2-ethylhexyl para-methoxycinnamate is mentioned. Para-methoxycinnamic ester-type ultraviolet absorbers have a defect of being insufficient in stability with time lapse on smell, color, etc., and as their stabilizer, butylhydroxytoluene (BHT) is usually used. However, on the other hand, there is a trend that the addition of a stabilizer is not preferred, and both of BHT-added preparations and BHT-not added preparations are sold on the market.
However, butylhydroxytoluene (BHT) which has hitherto been used is a component on which the duty of indication is assigned among stabilizers in the cosmetic field, and although BHT is a stabilizer expected on its effect, it has an aspect of being hard to accept on the market in view of safety. Further, when no stabilizer is added, it is known that the prescribed preparation starts to deteriorate at an early stage on smell and/or color, and usually, the influence on the prescribed preparation increases together with time lapse. Therefore, when an ultraviolet absorber containing no stabilizer was prescribed, a treatment such as masking gets necessary, but in prescription of no perfume, there is a problem that such a treatment is hard to make.
Therefore, development of stabilizers whose component indication is not compelled and which have high safety has been desired.